Flash lamp



July 9, 1957 R. M. ANDERSON 2,798,368

' FLASH LAMP Filed June 1. 1955 f. wf

Tot al Light A B PeaK Intensity ZZr `0 Kclo4 10o 9o Inventor:

Robert M. Anderson, Hfs Atrbo;nE ey FLASH LAlVIP Robert M. Anderson, Euclid, hio,vassignor to General Electric Company, a corporation ofpNew York Application `lune 1, 1953, Serial No. 358,785

8 Claims. (Cl. 67-31) My invention relates in general to flash lamps of the type commonly employedv for photographic purposes and which usually comprise a sealed light-transmitting bulb in which is enclosed suitable means for producing, upon ignition of the lamp, a momentary flash of actinic light. More particularly, my invention relates to ash lamps of the type disclosed and claimed in Pi'pkin Patent 2,291,- 983, dated August 4, 1942, in which the source of actinic radiation is constituted primarily by one or more beads or compact masses of fulminatingmateriall disposed within the glass bulb.

For many photographic picture taking purposes, it is desirable to employ a fiash 'lamp which is not only capabl'e of producing, a momentary flash of light of suffi'- cient intensity for taking pictures (e. g., at least around 8 to 9 million lumens peak intensity and at least around 4500 lumen seconds total light) but which will also peak at approximately the same extremely short interval of time following initial closure ofthe electrical circuit through the ignition filament of the lamp as the time interval normally required for the shutters of ordinary inexpensive type cameras to reach. theirA maximum opening after the actuation thereof,4 such/time interval usually being. around live milliseconds or so. Flash lamps of this general type are commercially available at present and are commonly known as primer or SMtype flash 'lamps such as disclosed in the aforementioned' Pipkin patent, the combustible material of such lamps consistingv of one or more beads of a fulminating or primer' material disposed on the inner ends of the lead-in wires of the lamp.

The fulminating or` light-giving material ofv such socalled primer type fiash lamps ordinarily comprises an intimate admixture of, one or more metal powders and one or more oxidizing agents or oxygen-liberating powders bonded together by a suitablebinder. nating material most commonly employed heretofore, however, has usually consisted" of an admixture of zirconium metal powder andi chemically pure potassium perchlorate and sodium chlorate powders bonded' together by a nitrocellulosev solution^preferably' one containing from 1/2v to 41A. percent solids.

The production of such primerl type flash lamps ernploying the above-described particular fulminating material composition incorporating both potassium perchlorate and sodium chlorate as oxidizing agents requires the exercise of exceedingly careful control' over the involved manufacturing processesV in order to notA only` insure that the lamps will possess the required flash performance characteristics but to also eliminate the possibility of dangerous lampexplosions on flashing: For one thing, the sodiuml chlorate componenty ofthe ful'rni'nating` material is inherently` of hygroscopic nature and thus tends tol absorb moisturey from the atmosphere; As a result, duringA cert-ain periods of the year, particularly during thesummer months when: highl humidity atmospheric conditions frequentlyprevail, the'absorption of moisture from the atmosphere by the fulrninatingmaterial' on' the The fulmilCC lamp mounts, prior to their sealing into the lamp' bulbs, becomes so great as to not only adversely affect' thelamp performance characteristics to such an extent as torender the lamps unsuitable for use but to also cause lamp explosions on flashing. For such reasons, therefore, it has been common practice heretofore to either discontinue the manufacture of this type flash lamp during such high humidity seasons of' the year or. else to con`` duct the entire operation of applying the fulminating material to the lamp mounts in an air-conditioned humidity-A controlled room, followed by sealing-in of the finished primered mounts into the lamp bulbs immediately upon removal from the air-conditioned room so that the ful-` minating or primer material. does not haveV sucientitime to absorb moisture from the surrounding atmosphere'.

There are certain other manufacturing disadvantages which attend the' production of primer type flash lamps with the above-mentioned' particular'- potassiumA perchlo` rate and sodium chlorate containing fulminating mate'- ri'al. Thus, such fulminat'ing compositions readily ignite by frictional contact, as when rubbed. across the least abrasive surface. It is therefore necessary during manufacture that the primered lamp mounts be carefully handled prior to the4 sealing-in thereofI into the lamp bulbs. Also, the quantity of suchfulminating material normally required in each lamp to produce the desired` levelA of light output therefrom is of` such amountas to cause a tendency of the fulminating material to bridge across the inner lead-in' wires andl consequently embedthe ig nition filament to such an excessive extentas to' ad-v versely affect or vary' the timingl ofthe lightfla'slr' so as to' render the lamp unsuitable' for use; In addition, with such particular fulminating composition, the preparation of the fulminating material is complicated' by thei fact that the. sodium chlorateand; potassium perchlorate pow; der components. thereof' must'beV mixed by. special vibration methods in order to assure aV homogeneous mixture ofthe two powders in the final admixture such' asis necessary to the production of uniformly acting primer beads and therefore uniformly performing flash lamps..

It is an object of my invention, therefore, to provide a ash lamp of the above-described' primer type having improved light performanceV characteristics and'whichv is rnoreuniform in operation;

Another object of my invention is to provide a't Hash lamp ofV the above-described primerv type in which the explosion hazard on charge flashing thereof is greatly reduced without any sacrifice in` the light'fiashperformance characteristics of suclr lamp:

Another object of my inventionr isv to provide a flash lamp of the above-describedl primer type which is'easier, safer and more economical to manufacture than previous flash lamps of` this general'type'.

According to one; aspectof the invention, Ihav'e found that the above objects are attained when the fulminating material of a primer type flash lamp is formed of' an admixture consisting essentially ofV from (iO-% by weight' of zirconium metalpowd'er and' from 204'0`% by weight' of potassium, perchlorate. powder bonded together by a suitable binder. K

According to a further aspectof the invention, the amount of such fulminating material'c present. within the lamp bulb is kept' within a predetermined. range of` the order of from 124 to. 2.6' mgs. per cc.` of bulb volume while the bulb i's filled with, oxygen ata pressure, less than approximately ZOG'mms. of"l mercury but; sufficient to provide enoughV free oxygen to amount',4 in combination with the combined"1oxygen present' in the fulrninating material, to at' leastl of the ord'er' of 90%'V ofthe. total oxygen required for complete combustion ofi, the.. zirconiumin the ful'minati'ng materialfwitln the, bulb, the amount of combined oxygen, furthermore, present' in the fulminating material within the lamp bulb being kept below approximately 65% of the total amount of oxygen present in the bulb.

Further objects and advantages of my invention will appear from the following detailed description of a species thereof and from the accompanying drawing, in which Fig. 1 is an elevation of a flash lamp comprising my invention, and

Fig. 2 is a chart showing the curves representing the time to peak, peak intensity and total light output of primer type flash lamps provided with fulminating materials composed of various percentages of zirconium and potassium perchlorate.

Referring to the drawing, the lamp according to my invention comprises a bulb or envelope l `of glass or other suitable light-transmitting material and provided with a relatively short neck portion 2 entirely enclosed and reinforced by a base 3 secured thereto. The bulb l is sealed and Iilled with a combustion-supporting gaseous filling, preferably oxygen at a suitable pressure below 200 mms. of mercury, as described hereinafter. To minimize cracking of the bulb on charge ashing and to render the bulb` substantially shatterproof, a suitable light-transmitting lacquer for varnish is coated on the inner and outer surfaces of the bulb. Sealed into the bulb I and extending thereinto from the neck portion thereof is a small and relatively short mount structure comprising a re-entrant stem 4 having a pair of leading-in conductors or wires 5, 5 sealed into the press portion 6 of the stern and extending therethrough to the contact terminals of the base 3. The leading-wires 5, 5 are provided with juxtaposed parallel inner lead portions 7, 7 which are interconnected by a filament 8 consisting of a straight length of wire of a suitable refractory material, preferably tungsten.

Disposed on the inner end or tip portion of each of the inner leads 7, 7 so as to partially embed and contact the filament 8, is a solid bead or compact mass of fulminating substance or combustible material 9 for pro ducing, upon ignition, a ash of actinic light of relatively high intensity. The fulminating material employed for the combustible beads 9 usually comprises an admixture of one or more sensitive metal powders and one or more oxidizing or oxygen-liberating powders bonded together by a suitable binder. Heretofore, the fulminating material most generally employed has consisted of an admixture of linely divided zirconium metal powder and finely divided potassium perchlorate and sodium chlorate powders bonded together by a binder comprising a nitrocellulose solution containing from 1/2 to 41/2 percent solids.

In accordance with the invention, I have found that by entirely eliminating the sodium chlorate ingredient from the above-described fulminating composition and proportioning the zirconium and potassium perchlorate powder components thereof within certain specified limits, While at the same time keeping the amount of free oxygen gas in the bulb below a predetermined pressure and the amount of combined oxygen in the fulminating material below a certain predetermined percentage of the total combined and free oxygen present in the bulb and also keeping the amount of fulminating material in the bulb within a predetermined weight range per unit volume of the bulb, the explosion hazard on dashing of the lamp is greatly reduced and, in effect, practically eliminated without any sacrifice whatever in the ash performance characteristics of the lamp, i. e., while still maintaining the required time to peak, peak intensity and total light performance characteristics thereof. To this end, the fulminating material of which the beads 9 are composed is formed of an agglutinated admixture consisting essentially of from 60-80% by weight of linely divided (approximately 325 mesh) zirconium metal powder and from -40% by Weight `of finely divided (approximately 325 mesh) chemically pure potassium perchlorate powder, bonded together by a binder such as nitrocellulose solution containing, for instance, from approximately 1/2 to 41/2 percent solids. The zirconium may be either of the type manufactured by the Foote Mineral Company of Philadelphia, Pennsylvania, and commercially known as their grade 120A, or of the type manufactured by Metal Hydroxides Inc. of Beverly, Massachusetts, and commercially known as their grade AZ.

By keeping the percentages by weight of the zirconium and potassium perchlorate components of fulminating material within the above-mentioned ranges, the flash performance characteristics of the lamp are at least as good as or better than those of the previous primer type flash lamps provided with fulminating material employing both potassium perchlorate and sodium chlorate as oxidizing agents. For example, the time to peak of the light iiash produced by the lamp according to the invention will occur at the required time interval of around l1/z to 5 milliseconds following initial closure of the electri cal circuit through the ignition lament 8 of the lamp. This is evident from curve A of Fig. 2 showing the time to peak of primer type ash lamps having differently proportioned zirconium and potassium perchlorate containing fulminating materials, the total oxygen present in the bulbs in each case being approximately equal to that theoretically required for complete combustion of the zirconium in the primer beads. lt is apparent from curve A that when the proportion of zirconium and potassium perchlorate falls appreciably outside the abovespecilied limits of 2040% potassium perchlorate and 60-80% of zirconium, the time to peak of the light flash is increased beyond the 5 millisecond maximum time interval specification therefor so that the lamp then becomes too slow to be suitable for the intended purpose. Likewise, as shown by curve B in Fig. 2, the peak intensity of the light Hash produced by the various types of lamps charted in curve A reaches a maximum, for the abovcspecied particular primer composition range of 20-40 potassium perchlorate and 60-80% zirconium, which fullls and in most cases exceeds the 8 to 9 million lumen minimum peak intensity requirement for such primer type liash lamps. Also, the average total light output of those lamps whose fulminating material composition is within the above-mentioned range of 20-40% potassium perchlorate and 60-80% zirconium fullls the minimum requirement of 4500 lumen seconds total light for such primer type lamps.

In particular, I have found that by using the fulminating composition Whose zirconium content is near the upper end of the said range, e. g., around 75% zirconium and 25% potassium perchlorate, it is possible to produce a primer type flash lamp which, while utilizing from 2025% less Weight of fulmiuating material than that formerly employed (which reduction amounts to a 10% saving in zirconium and a 50% saving in oxidizing niaterial) will nevertheless produce more than 10% greater total light output Without any sacrice whatever in the time to peak or peak intensity of the lamp.

In order to obtain the maximum amount of actinic light from the fulminating material enclosed within the lamp bulb 1, suiiicient oxygen should be present in the bulb to insure substantially the complete combustion of all the zirconium present in the beads 9 of fulminating material. Thus, the total oxygen present in the bulb (i. e., the total of the free oxygen gas in the bulb and the combined oxygen present in the primer beads 9) preferably should amount to at least of that theoretically required for the complete combustion of all the zirconium present in the primer beads 9.

In addition to obtaining the above-mentioned improved light performance by the use of fulminating material compositions according to the invention, I have found that by maintaining certain other conditions within the lamp, the possibility of an explosion thereof on charge flashing is greatly minimized and practically eliminated. To achieve this end, the total amount of combined oxygen arcanes present in the primer beads 9 rin the bulb should be kept below that percentage of the total amount. of' combined and free oxygen in the bulb which would cause the combustion. of the primer beads 9 to proceed with such forcefulness as to be likely t'o cause an explosion of the glass lamp bulb. The greater the proportion of the oxygen in the fulminating material, the more forceful will be the combustion of the primer 'beads It has been found that by keeping the total' amount of cornbined oxygen in the primer beads 9 in the bulb below 65%, and preferably below about 40% that of the total combined and free oxygen present in the bulb', the force ofthe combustion of the primer beads 9 is maintained within safe limits wherein it is not likely to cause an explosion of the glass lamp bulb. In any event, however,l the pressure of thev oxygen gasv lling in the bulb should not exceedl of the order of about 200 mms. of mercury since with higher pressures the resulting gas pressure developed in the lamp bulb on flashing would be excessively high such 'as 'would then be likely to cause an explosion of the glass lamp bulb.

A further necessary condition to the production of substantially explosion-proof primer type flash lampsy according to the .invention is the requirement that the total charge `or weight of fulminating material 9 in the bulb 1 be kept below that amount thereof which would normally cause the combustion of the primer beads 9v to take place too forcefully with consequent excessive tendency to cause -an explosion of the glass lamp bulb. In accordance with the invention, I have found that by keeping the total amount of fulminating material 9 in the bulb below approximately 2.6 mgs. per cc. of bulb volume, the force of the combustion ofthe primer beads 9* is maintained within reasonably safe limits such as are not apt to causelamp bulb explosions on charge flashing. The total amount of fulminating material used, for the primer beads 9 in the bulb I should' not be s'o little, however, as to prevent the generation of the required level` of light output by the lamp. .For such reasons, therefore, it ispreferred that the total weight of fulminatingV material 9- present in the bulb 1 should' amount to at least of the order of 1.4- mgs. .per cc.. of bulb volume.

Flash lamps made in `accordance with the invention as described hereinabove have been found to be remarkably free from dangerous explosions on lamp hashing. When subjected to the conventional factory test which is normally employed to ascertain theV safety'oflash lampsrfrom explosion (such, test Ibeing conducted under conditions which are muchmore severe and conducive to lamp explosions than are normally encountered in actual service), primer type hash lamps according to the invention have shown a 90% reduction-in the number ofy explosions as compared tothe previous form of primer type- 'ash lam-p heretofore in use and employing both potassium perchlorate and sodium chlorate in the fulminating material as oxidizing agents. For example, comparative factory tests conducted on large numbers of such ash lamps conclusively show that with lamps constructed according -to the invention the percentage `of lamp explosions on flashing is only around one-tenth that which is encountered with the previous form of primer type ash lamp, based on a reduction in the percentage of lamp explosions of from around 0.85% to 0.08%.

As a specic example of a flash lamp constructed according to the invention, the bulb 1 is of the small type commercially known zas a B11, such as customarily used for primer type ash lamps heretofore, and having an internal volume, when finished into a lamp, of approximately 25 cc., exclusive of the stem 4 and other internal parts of the lamp. The beads 9 of combustible material are composed of from 40-55 milligrams total of a fulminating material composition -according to the invention containing of the order of 75% zirconium and 25% potassium perchlorate, and the bulb is lled with oxygen to a pressure of l50170 mms. of mercury. Flash lamps of this specific construction, besides lbeing substantially free from lamp explosion on flashing, produce a total light output averaging more thany S000 lumen seconds, representing an increase of more-than 10% over the previous type of primer flash lamprheretofore in use, and apeak intensi-'ty averaging from 87.5 to 9.5 million lumens and peaking at around 4.7 to 5.0 milliseconds following closure ofthe electrical circuit through the ignition circuit 8of` the lamp.

=In -addition to their improved light ,performance characteristics and their practically explosion-proof character, flash lamps accord-ing to the invention .are more uniform in operation and are easier, safe and `less expensive to manufacture as compared to previous flash lamps of this type employing sodium chlorate in the primer beads 9'; Thus, since the lamp Aaccording to the invention requires only about three-fourths as much fulminatingy material 9 in each lamp as formerly employed in such previous type primer flash lamps (e. g., 45 milligrams as compared to 60 milligrams previously) to produce equal or better light output, the tendency of the fulminating material to lbridgel across thev inner leads7, 7 at the region ofthe lamen't 8, d-uring the dipping of the mounts to apply the primer beads 9 thereto, is proportionately minimized. Such bridging of the fulminating material results in excessive embedding of the ignition filament 8- in fulminating material '9 which then acts to slow down or vary the heating of the filament 8 when energized, with consequent variation in the ignition of the fulminating material 9 and inthe timing Yof the light flash. By minimizing Vthe bridgi'ng" of the fulminat-ing material 9 across the inner leads 7, 7 through the use of a smaller total amount of fulminating material in each lamp, the lamps according tothe invention are thereby rendered more uniform in action, particularly in respect to their timing. The reduction in 4the amount of fulminating material 9 required for each lampalsoaffords the economic advantage of'enabling the production ofV over 10% more lamp mounts from av given quantity of fulmina-ting material.

As stated previously, with the primer type flash lamps previously in use employing sodium chlorate in the fulminating material 9, it was found necessary, because of the hygroscopic nature of the sodiumchlorate, either to entirely discontinuelthe manufacture of -such lamps during high humidity seas-onsv of the year or else to conduct the voperation of applying the primer beads 9` to the lamp mounts in a htunidity-controlled air-conditioned 4room followed by immediate sealing of the primered mounts into the lamp bulbs to prevent the absorption by the .primer beads 9 of moisture from the surrounding atmosphere. The elimination, in accordance with the invention, of sodium chlorate from the `fulminating material 9 therefore 'avoids the necessity for taking any such` specialY precaution of conducting the primer -bead applying operation only in moisture-free surroundings, and permits such operation to be conducted instead under normal room conditions and at any season of the year, regardless of the prevailing atmospheric humidity condition and without causing any deleterious eect on the light performance characteristics of the lamp or increasing the explosion hazard thereof.

Whereas the previous sodium chlorate containing fulminating compositions employed for primer lamps will flash from friction upon being drawn or rubbed across an abrasive surface, the fulminating material according to the invention, having no sodium chlorate therein, will not hash but instead will merely crumble under such abrasive action. As a result, not only the fulminating material itself according to the invention, but the primered lamp mounts as well, are safer to handle. Also, the fulminating material according to the invention is easier than the prior type fulminating material containing sodium chlorate in that it does not require the use of special vibration methods to effect the mixing of the powder ingredients into a homogeneous admixture so as to insure uniformly acting primer beads.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A fiash lamp `comprising a sealed bulb containing a combustion-supporting gaseous filling, a pair of leadingin conductors extending into said bulb, a filament connected across said leading-in conductors, a compact body of fulminating material within said bulb in position to be ignited upon heating of said filament, said fulminating material constituting substantially the sole source of actinic radiation produced by tbe lamp and comprising an admxture consisting essentially of finely divided zirconium metal and potassium perchlorate powders bonded together by a binder, the zirconium and potassium perchlorate being present in said admixture in proportions by weight ranging approximately from 6080% zirconium and 40-20% potassium perchlorate.

2. A ash lamp comprising a sealed bulb containing a combustion-supporting gaseous filling, a pair of leadingin conductors extending into said bulb, a filament connected across said leading-in conductors, a compact body of fulminating material within said bulb in position to be ignited upon heating of said filament, said fulminating material constituting substantially the sole source of actinic radiation produced by the lamp and comprising an admixture consisting essentially of finely divided zirconium metal and potassium perchlorate powders bonded together by a binder, the zirconium and potassium perchlorate being present in said admixture in proportions by weight of the order of 75% zirconium and 25% potassium perchlorate.

3. A flash lamp substantially as set forth in claim 1 wherein the said combustion-supporting gaseous filling consists of oxygen at a pressure less than 200 mms. of mercury.

4. A ash lamp substantially as set forth in claim 1 wherein the said combustion-supporting gaseous filling consists of oxygen and wherein the weight of the combined oxygen in the said fulminatng material is less than about 65% of the total weight of combined and free oxygen present in the bulb.

5. A flash lamp comprising a sealed bulb, a pair of leading-in conductors extending into said bulb, a filament connected across said leading-in conductors, a compact body of fulminating material within said bulb in position to be ignited upon heating of said ilament, said fulminating material constituting substantially the sole source of actinic radiation produced by the lamp and comprising an admixture consisting essentially of finely divided zirconium metal and potassium perchlorate powdexts bonded together by a binder, the zirconium and potassium perchlorate being present in said admixture in proportions by Weight ranging approximately from -80% zirconium and 4020% potassium perchlorate, and a filling of oxygen gas in said bulb at a pressure below 200 mms. of mercury, the total weight of the combined and free oxygen present in said bulb being at least of the order of that required for complete combustion of all the zirconium in said fulminating material and the weight of the combined oxygen in said fulminating material being less than about of the total weight of combined and free oxygen present in the bulb.

6. A fiash lamp substantially as set forth in claim 5 wherein the total quantity of fulminating material in said bulb amounts to from 1.4 to 2.6 mgs. per ce. of bulb volume.

7. A flash lamp comprising a sealed bulb having an internal volume of the order of 25 cc., a quantity of fulminating material supported therein and constituting substantially the sole source of actinic radiation emitted by the lamp, electrical ignition means comprising a filament in said bulb having at least a portion thereof in contact with said fulminating material for developing an ignition temperature therein upon energization of the filament, said quantity of fulminating material having a weight ranging from 40-55 mgs. and consisting essen tially of an admixture of the order of by weight zirconium metal powder and 25% by weight potassium perchlorate powder bonded together by a binder, and a lling of oxygen in said bulb at a pressure of the order of from -170 mms. of mercury.

8. A flash lamp comprising a sealed bulb having an internal volume of the order of 25 cc., a pair of lead-in wires extending into said bulb, a filament bridging said lead-in wires, a compact quantity of fulminating material adhering to each of said lead-in Wires and in contact with said filament so as to be ignited thereby upon heating of the filament, said fulminating material constiuting substantially the sole source of actinic radiation produced by the lamp and consisting essentially of from 40-55 mgs. total of a finely divided powder mixture of the order of 75% by weight of zirconium metal powder and 25% by weight potassium perchlorate powder bonded together by 'a binder, and a filling of oxygen in said bulb at a pressure of the order of from 150-170 mms. of mercury.

References Cited in the file of this patent l UNITED STATES PATENTS 2,291,983 Pipkin Aug. 4, 1942 2,361,495 Pipkin Oct. 31, 1944 2,375,742 Kalil May 8, 1945 OTHER REFERENCES Comprehensive Treatise on Inorganic and Theoretical Chemistry, volume 2, page 325, by J. W. Meller, 1922. 

1. A FLASH LAMP COMPRISING A SEALED BULB CONTAINING A COMBUSTION-SUPPORTING GASEOUS FILLING, A PAIR OF LEADINGIN CONDUCTORS EXTENDING INTO SAID BULB, A FILAMENT CONNECTED ACROSS SAID LEADING-IN CONDUCTORS, A COMPACT BODY OF FULMINATING MATERIAL WITHIN SAID BULB IN POSITION TO BE IGNITED UPON HEATING OF SAID FILAMENT, SAID FULMINATING MATERIAL CONSTITUTING SUBSTANTIALLY THE SOLE SOURCE OF ACTINIC RADIATION PRODUCED BY THE LAMP AND COMPRISING AN ADMIXTURE CONSISTING ESSENTIALLY OF FINELY DIVIDED ZIR- 